Early work on hip prosthesis showed that the metal component would loosen in bone even when screws were used. This practice resulted in the death and resorption of the bone; thus cement was used in orthopedic surgery for firm implantation of prostheses. In recent years antibiotics have been added to the cement as a prophylaxis against infection. This research investigates the effects of antibiotics on the diametral tensile and compression strength of the cement. Samples made with 2 g of antibiotic per surgical packet of bone cement containing the antibiotics gentamicin, keflin, and a combination of the two were tested. These samples were aged at ambient temperature for periods of 1 day and 1, 2, 8, 13, and over 30 weeks. A stastical analysis using a two-way analysis of variance with interaction was conducted. It was concluded that the compression strength was affected by the antibiotic, and not by the aging period, but that there is an antibiotic-aging period interaction. The tensile strength is not affected by either the antibiotic or the aging period, and there is an antibiotic-aging period interaction. Current work being conducted will analyze additional factors and interactions.